INFICON LDS3000 Modular Leak Detector Interface description - Manual (Page 7)

ASCII Protocol 7
2 ASCII Protocol
2.1 Comparison between ASCCI- and LD protocol
ASCII- and LD protocol have nearly the same functional range, but each of them
have some advantages and disadvantages :
ASCII protocol:
Advantages:
• human readable
• easy to use with simple terminal program
Disadvantages:
• No checksum, therefor lower data security
• PC/ PLC software must convert numerical values from ASCII string to binary
• Lower efficiency (for example: 8 data bytes for one float value)
LD protocol:
Advantages:
• Leak detector status always transmitted in each slave telegram
• High data security due to CRC checksum
• Binary transmission of numerical values – no conversion needed in PC/ PLC
software
• High efficiency (for example: 4 Byte data bytes for one float value)
Disadvantages:
• Not human readable
• Not useable with simple terminal program
2.2 Communication Parameters
2.3 Command Format
In ASCII protocol any command starts with « * » (ASCII code 42dec/2Ahex) and is
finished with the end sign CR (ASCII code 13dex/0Dhex). There is no differentiation
between upper and lower case. A blank is required between the command and the
parameter, no other blanks are allowed.
There is a short and an extended form of the command. Either the short or the
extended command must be used, no other abbreviations are allowed (The short
form is here written in capitals but the SW don’t difference upper and lower cases).
Command Words have to be separated by a colon. A command can be composed
of up to three words. Parameters have to be separated by a comma.
Data format
Baudrate
19.200, 8 data bits, 1 stop bit, no parity